Fibers of polyamides typified by nylon 6 (hereinafter may be referred to as “N6”) and nylon 66 (hereinafter may be referred to as “N66”) and fibers of polyesters typified by a polyethylene terephthalate (hereinafter may be referred to as “PET”) and a polybutylene terephthalate (hereinafter may be referred to as “PBT”) exhibit excellent mechanical properties and/or dimensional stability and are widely used not only for clothing but also for interior decoration, vehicular interior decoration and industrial use.
Fibers of polyolefins typified by a polyethylene (hereinafter may be referred to as “PE”) and a polypropylene (hereinafter may be referred to as “PP”) are light-weighted and are widely utilized for industrial use.
However, in any kind of fibers, fibers each comprising a single polymer have some limitations in the properties thereof. Attempts have therefore been made to modify such polymers typically by copolymerization or polymer blending or to compound functions typically by multi-component fiber spinning or combined-filament spinning.
Among them, polymer blending has been actively investigated, since this technique does not require new designing of polymers and such a polymer blend can be produced by using a mono-component spinning machine.
Separately, hollow fibers and porous fibers have been investigated in order to reduce the weight of fibers or to impart water-adsorptivity thereto.
Attempts have been made to provide hollow fibers having high hollowness, but such hollow portions may be crushed, for example, as a result of false twisting. To avoid this, multi-islands hollow fibers, wherein a multitude of islands parts constitutes a hollow portion, using a conjugated fiber with a water-soluble polymer have been developed. In such fibers, the hollow portion generally has a diameter of 1 μm or more, the interface between the polymer and the air in the hollow portion significantly reflects visible radiation, and the resulting fiber cannot satisfactorily develop a color.
Porous fibers each having a multitude of pores on the order of sub-micrometers have been investigated. Such porous fibers have generally been produced not by multi-component fiber spinning but by polymer blend spinning.
Japanese Unexamined Patent Publication (Kokai) No. 2-175965, for example, describes a technique of blending a nylon with a PET copolymerized with a hydrophilic group, forming a fiber from the blend, and dissolving off the copolymerized PET from the fiber to thereby obtain a porous nylon fiber. The fiber of the invention has surface depressions and protrusions and/or pores on the order of submicrometers and has pearly luster. However, this fiber shows significantly deteriorated color property. This is because the fiber has a multitude of pores having a size on the order of wavelengths of visible radiation and thereby invites significant scattering of visible radiation even as compared with the multi-islands hollow fiber.
Japanese Unexamined Patent Publication (Kokai) No. 56-107069 (pages 1-3) describes a fiber having pores with a size smaller than visible radiation. In actual fact, however, the resulting fiber also shows significantly deteriorated color property, since the blend fiber contains coarsely aggregated PET particles, and the aggregated particles are dissolved off to form coarse pores each having a size on the order of submicrometers to one micrometer. In fact, above-mentioned Japanese Unexamined Patent Publication (Kokai) No. 56-107069 describes “most of the polyester component exists as lines with a diameter of 0.01 to 0.1 micron and there remain hollows substantially having the above-mentioned size in the polyamide” in line 7, in the left upper column of page 2, suggesting the presence of aggregated PET particles.
In addition, certain porous fibers using a nylon/PET blend fiber are described in Japanese Unexamined Patent Publication (Kokai) Nos. 8-158251 and 8-296123. These fibers, however, show a large variation in size of dispersed particles of PET in the nylon, for example, about 0.1 to 1 μm and cannot improve decreased color property caused by coarse pores. In addition, when the distribution of pore size is large as in the conventional techniques, coarse pores play an extremely increased role in the pores and, in contrast, nanopores do not play such a role. Thus, the porous fiber does not sufficiently exhibits advantages of the pores.
Demands have therefore been made to provide porous fibers substantially free from such coarse pores.
Separately, a variety of polymer alloy fibers serving as precursors for porous fibers and ultrafine yarns have been investigated.
U.S. Pat. No. 4,686,074 (page 28), for example, describes that an ultrafine PET fiber having a size of 9.4×10−5 deniers is obtained using a static mixer according to calculations and discloses a polymer alloy fiber having an islands-in-sea structure and comprising a polystyrene (hereinafter may be referred to as “PS”) as a sea part and PET as islands parts.
This document, however, mentions that an actually measured mono-filament fineness of the ultrafine PET fiber varies from 1×10−4 deniers to 1×10−2 deniers, showing that the resulting polymer alloy fiber includes dispersed particles of the islands parts PET with a diameter of 100 to 1000 nm and thus contains many coarse islands.
Japanese Unexamined Patent Publication (Kokai) No. 8-113829 (pages 1-12) discloses a very special polymer alloy fiber comprising a copolyester blended with 30% by weight of a polyether imide (hereinafter may be referred to as “PEI”), which copolyester comprises PET copolymerized with 10% by mole of an ethylene naphthalate component. In this fiber, PEI is dispersed as particles with a size on the order of 2 to 80 nm. The fiber, however, invites unstable spinning to thereby obtain yarns with large unevenness and lacks practical utility, because PEI is dispersed as particles in the fiber.
According to the invention disclosed in above-mentioned Japanese Unexamined Patent Publication (Kokai) No. 8-113829, spinning is carried out at a temperature of 320° C. in accordance with the melting point of PEI, which is excessively high for the copolyester, to thereby cause remarkable thermal decomposition. In an experiment for corroboration, the resulting polymer alloy fiber has a strength less than 1.5 cN/dtex and is not usable in practice. The invention disclosed in Japanese Unexamined Patent Publication (Kokai) No. 8-113829 also provides a spongy fiber having pores connected with each other by treating the polymer alloy fiber with a base in a 6% NaOH solution at 90° C. for 2 hours. The resulting yarn, however, has a strength less than 0.5 cN/dtex and is not practically usable from this viewpoint of strength, because both PEI and the copolyester have been hydrolyzed in the fiber.